other

Question 1

what is forensic art?

Answer 1

Art used in conjunction with legal procedures -
used for:
- the identification, apprehension or conviction of offenders
- the location of victims
- identification of unknown deceased persons

Question 2

4 guidlines of facial identification compositions (as stated in ACPO guidlines section 4.1.1)

Answer 2

• any notes and sketches produced during the production of an image are subject to disclosure.
• final composite must be signed and dates by both the witness and practitioner.
• declaration must be attached tot the composite image to warn handlers that any editing or altering of the composite is tampering with evidence.
• signed and dated sompositions become exhibits.

Question 3

what are the main forensic art techniques used in the UK?

Answer 3

1. composite facial sketching
2. facial reconstruction
3. age progression
4. crime scene illustration
5. injury depiction

Question 4

brief description of the forensic art technique: composite facial sketching

Answer 4

This involves interviewing witnesses to gather information about a suspect’s appearance and then creating a composite drawing that incorporates those features.

Question 5

brief description of the forensic art technique: facial reconstruction

Answer 5

This technique is used to recreate the facial features of a deceased person, often from skeletal remains or 3D scans.

Question 6

brief description of the forensic art technique: age progression

Answer 6

This technique helps visualize how an individual’s appearance may change over time, aiding in the location of missing persons or the identification of potential suspects.

Question 7

brief description of the forensic art technique: crime scene illustration

Answer 7

detailed sketches and illustrations of crime scenes, helping investigators understand the layout and identify evidence relationships.

Question 8

brief description of the forensic art technique: injury depiction

Answer 8

artistic documentation of injuries, helping to compare medical reports with witness descriptions and provide a visual record of trauma.

Question 9

how to calculate corresponding compression ratio of an image

Answer 9

divide the original file size (uncompressed) by the compressed file size (then put answer in front of :1 ).

Question 10

how many bits in a byte

Answer 10

8

Question 11

convert byte to kbyte

Answer 11

divide by 1000

Question 12

what is a JPEG ghost?

Answer 12

a visual artifact that can appear in JPEG images, especially when an image has been manipulated or spliced

Question 13

how are JPEG ghosts detected?

Answer 13

By analysing the DCT (Discrete Cosine Transform) coefficients of a JPEG image, the presence of different compression qualities can be identified and the manipulated region can be localized

Question 14

What is the transformation method used in JPEG image
compression?

Answer 14

DCT - Discrete cosine transformation

Question 15

How does discrete cosine transformation work?

Answer 15

This method converts the image from its spatial representation (pixel values) to a frequency domain representation. This allows for the identification and discarding of less important high-frequency components, reducing file size without significantly impacting perceived image quality.

Question 16

what is the difference between pure steganography and secret key steganography?

Answer 16

Explain the difference between pure steganography and secret key
steganography

Question 17

what is cryptanalysis?

Answer 17

cryptanalysis is the process of deciphering a code without being given a key.

Question 18

what is a common hashing algorithm/function? and what are three key properties for the output?

Answer 18

SHA-1
three key properties:
- fixed length
- digest unique to data message
- impossible to recover original message from message digest alone.

Question 19

what is a symmetric key?

Answer 19

the same key is used for both encryption and decryption

Question 20

what is an asymmetric key?

Answer 20

the key for encryption is different to the one used for encryption.

Question 21

how do vigenere cyphers work?

Answer 21

encryption:
1. line up the key under the message so the letters line up (if message is longer than key repeat the key until the end of the message).
2. change the letters for the numbers, numbering them using the placement of the numbers in the alphabet (A = 0).
3. add numbers together. if number above 25, minus 25.
decryption:
do the same but minus the numbers of the keyword from the numbers in the encrypted text.

Question 22

how does the transposition method work for encrypting and decrypting a message?

Answer 22

Encryption:
1. assign the keyword numbers according to the order they appear in the alphabet.
2. write the message beneath he keyword, lining up the letters and ignoring spaces.
3. write the letters out in the order of the numbers in the keyword.
decryption:
do this backwards.